US Dollars are accepted almost everywhere in Tanzania. There is no need to exchange your US Dollars into Tanzanian Shillings while in Tanzania. However, by paying with US dollars you will experience slightly less buying power. Most merchants will round up to the nearest dollar when doing a currency conversion. For example, if a bottle of water is 1700 shillings and the current conversion is 1900 shillings to one US dollar. They will charge you one full dollar for the bottle of water.